Allergic conditions such as asthma characteristically result in the recruitment of predominantly eosinophils and T cells but not neutrophils. The mechanisms by which this selective recruitment occurs is the focus of this proposal. The elucidation of these mechanisms may provide new targets for therapeutic intervention in asthma and other allergic diseases. Leukocytes are targeted to the endothelium at sites of inflammation by endothelial cell adhesion receptors. One of these receptors, vascular cell adhesion molecule-1 (VCAM-1), is expressed on the endothelium in allergic inflammation and interacts with alpha 4 integrins on the surface of the leukocytes. Alpha4 integrins are found on all leukocytes except neutrophils. In vivo data confirms that the interaction between VCAM-1 and alpha4 integrins is at least in part responsible for the pattern of leukocyte infiltration observed in allergic inflammation. We have previously demonstrated that VCAM-1 expression is regulated by the combination of TNF-alpha and IL-4, and it has been shown in vivo that this cytokine combination causes selective expression of VCAM-1 on the endothelium and an alpha4-integrin-positive leukocyte infiltrate. Elevated TNF is found in many inflammatory conditions. However, IL-4 is specifically increased in allergic diseases where it selectively induces VCAM-1 expression. We have previously demonstrated that TNF increases transcription of the VCAM-1 gene through two adjacent kappaB sites. Unlike other kappaB sites, these sites mediate an endothelial-specific response to TNF. IL-4 acts in concert with ; synergistically increasing VCAM-1 expression by increasing the half-life of VCAM-1mRNA. IL-4 causes two important changes in the pattern of VCAM-1 expression:it allows concentrations of TNF that do not normally cause increased expression of EC adhesion molecules to activate VCAM-1 expression, and it substantially prolongs the expression of VCAM-1 at sites of allergic inflammation. IL-4 mediated stabilization of VCAM-1 mRNA occurs through a unique mechanism that does not involve the classic JAK/STAT pathway of IL-4 activation which has been well studied in T cells. Thus it is likely that the combination of TNF and IL-4 result in the infiltration of eosinophils and T cells specifically in allergic diseases. We propose studies to examine the molecular mechanisms of how this "allergic cytokine" combination regulates VCAM-1 expression.